1. Field of the Invention
The present invention relates to a timepiece having a date display function.
2. Description of the Related Art
A common date display mechanism used in wristwatches and other types of timepieces has a ring-shaped display panel called a day wheel. The numbers 1 to 31 are evenly spaced around the circumference of the day wheel, and the day wheel is rotationally driven linked to the gear train for rotationally driving the hour hand for displaying the hour. For example, when the hour hand is turned the equivalent of 24 hours by the gear train, the day wheel turns a distance equal to one day (that is, a 360/31 degree angle of rotation), and a number corresponding to the date is displayed in the date window provided in the dial of the wristwatch.
A problem with this simple date display mechanism is that at the end of the month in months shorter than 31 days in the solar calendar (that is the short months of February, April, June, September, and November), a non-existent date that is not actually on the calendar is displayed. Japanese Patent Laid-Open Publication (kokai) H5-142362 teaches a mechanical timepiece with a so-called perpetual calendar function achieved using a combination of gears. Between the gear train and day wheel this mechanical timepiece has multiple gears combined to drive the day wheel according to the date in each month of a four year period including a leap year so that non-existent dates are not displayed. A problem with this mechanical timepiece is that many more gears than typical are required, resulting in a complicated mechanism and high production costs.
To solve this problem attention has recently focused on electronic timepieces having a date display mechanism consisting of an integrated circuit (IC) device as a controller, a storage device for storing calendar information denoting the year, month, and day, an actuator controlled by the IC device, and a day wheel rotationally driven by the actuator. The IC device has an evaluation function for determining if the date indicated by the calendar information is a non-existent date. By displaying the date based on the result passed by this evaluation function, non-existent dates are not left displayed in the date window, and the correct calendar date is thus displayed.
A problem with such electronic timepieces is that the user must adjust the calendar information to the actual date if the date displayed in the date window becomes different from the actual date as a result of replacing the battery. More specifically, when the battery of an electronic timepiece powered by a primary cell is replaced at a jeweler or watch dealer, the jeweler, for example, adjusts the calendar information. With an electronic timepiece powered by a secondary cell, the user adjusts the calendar information after charging the battery. It is assumed below that primarily the user adjusts the calendar information.
A problem with this electronic timepiece is that if the date displayed in the date window is offset much from the actual date, the actuator must rotationally drive the day wheel a corresponding distance to adjust the date, and this consumes much power. If much power is consumed to adjust the date in an electronic timepiece powered by a secondary cell in particular, the resulting voltage drop could cause the electronic timepiece itself to stop.
A further problem is that it takes a while to finish adjusting the date if the actuator must rotationally drive the day wheel very far.
A yet further problem with this electronic timepiece of the prior art is that adjusting the calendar information stored in the IC is difficult and complex. For example, in order to adjust the calendar information in this prior art electronic timepiece the user must first manipulate the crown or other operator to set the date displayed in the date window to a specific reference date (such as January 1 of a leap year), then apply a calendar information initialization command to the IC in order to set the stored calendar information to the displayed date (that is, reset it to a reference position). The user then sets the current date as the displayed date.
In a conventional electronic timepiece having a display window for displaying only the day, the year and month are generally displayed by the movement of the hands in a manner similar to how the hour hand and minute hand are displayed.
When the displayed date and the actual date are offset in a conventional electronic timepiece as described above, the user must perform an adjustment sequence such as described above, and this operation can be extremely complicated. Furthermore, adjusting the calendar information is particularly difficult if the user forgets this adjustment procedure.